The present invention relates to an improved valve component for a plate-type non-return valve and particularly although not exclusively relates to an improved valve plate and improved non-return valve incorporating such improved valve plate.
Plate-type non-return valves are well known and include a valve body or seat produced by casting, forging or milling and having annular slots therein, a valve closure means which is a valve plate having "kidney shaped" or annular slots therein in regions which are not to overlie the slots in the valve seat, and a valve stop or guard comprising a body having annular slots therein generally corresponding to but not aligned with the slots of the valve seat. The valve plate is normally clamped at a central region between the valve guard and seat although there is sufficient clearance between the seat and guard in the region of the slotted portion of the valve plate to permit displacement of the valve plate during the operation of a compressor or the like so as to lift off the valve plate from the valve seat and allow air to pass through annular slots in the valve seat plate and thence through the annular slots in the valve plate and through the slots in the guard plate. In use, following the opening of a valve by creation of a sufficient pressure differential between the inlet and outlet sides of the valve, a change in the pressure differential is created which enables the valve plate to return by virtue of the back-pressure of the air and the natural resilience of the metal of the plate clamped in its central region and possibly assisted by additional spring means or plate type springs so that the valve plate closes the slots in the valve seat and thus act as a non-return valve. To ensure a smooth and efficient operation of the valve, damper plates may also be provided. The plate type springs and damper plates often also have central flexible spring or guide arms which are clamped between the valve seat and guard. Many prior devices of this type of valve have been disclosed and, purely by way of example, reference is made to British Patent Specification Nos. 438139, 1140633 and 1406278.
It is important in the design of the valve plates (and other plates) to provide a plate which has a high "lift" and thus high efficiency whilst at the same time ensuring that the flexing and bending necessary for achieving of the high lift do not result in a shortened life of the component as a result of fatigue and breakage. It is furthermore important in the production of a valve plate to produce a plate which is as free as possible from undesirable stresses in the material thereof. It is still further important that the valve plate be provided with optimum area of through passage for the flow of air for increased efficiency.
Generally, all hitherto known valve plates of circular outline have a continuous outer periphery and annular concentric passages or slots running between normally radially extending webs interconnected with the concentric rings of the metal plate forming the valve closure portion. In the central regions of known plates there exists a concentric circular portion or arcuate portions forming a hub for the mounting by clamping of the plate between the valve seat and valve guard and the interconnection between the innermost, concentric main closure ring and the central mounting hub is by way of one, two or at a maximum three connecting spring or guide arms which each consist of an arcuate portion concentric with the plate and having a straight portion or a portion which is formed by cutting a straight slot through a radial web interconnecting the rings and which slot is defined by a straight edge or straight edges. Reference will be made herein to "guide arms" and it should be understood such term is to cover flexible spring or connecting arms of components other than valve plates, i.e. cushion or damper plates and plate type springs. As mentioned these straight edge portions of the guide arms are generally formed by a straight slot extending either radially or inclinedly across a radial web. Whilst many variations in disposition and size have been proposed these generally comprise the essential characteristics of known valve plates. Certain spring or cushion (damper) plates have been proposed which are normally located between the valve plate and guard plate and act on the valve plate in resilient manner to provide for improved performance of the valve. It is known from Canadian Patent Specification No. 573260 for a cushion plate to have a portion with straight, radially, extending support arms and with two small slots being provided in the outer circular periphery to allow for relative deflection.